The invention relates to a process and apparatus for surveying a railway track for any deviation from a track survey plan having values which set forth the desired course or path of the track relative to reference marks each having light reflectors located on upstanding supports in the vicinity of the track.
A part of the procedure for maintaining railway tracks the course or path of the track must be accurately measured, compared with the predetermined and desired course values of a track survey plan, and thereafter corrected for any deviations from the values of the survey plan. Track maintenance equipment that may be utilized for this purpose are usually very large and complex structures capable of traveling along the track and capable of removing, for example, existing rail sections and installing new rail sections which may include cleaning the ballast. The equipment moves slowly and continuously along the track as it performs these track maintenance operations. The position of the equipment and therefore the course or path of the track must be measured relative to reference marks located along and adjacent the track, usually on upstanding supports for catenary electric power supply lines provided for electrically driven locomotives. Of course, for diesel-only railway lines, other upstanding supports are arranged along the tracks to which the reference marks are mounted.
With the presently available track surveying systems, the track course measurement is carried out by means of optical devices usually through the use of a separate reference device relative to the equipment. These reference devices are located along the track at predetermined distances from the maintenance equipment and the position of the equipment relative to the reference marks is determined, i.e., measured. During such distance measurement, both optical angular position measuring devices and tape measures are used. However, this type of measurement is very time and operator intensive, since the reference device must be repeatedly assembled and disassembled, and several measurements are required to determine a single position to keep the interruption intevals, which are necessary for changing the measurement from one reference device to the other, to a minimum. And, several such devices, which are repeatedly assembled and disassembled, are simultaneously required.